Field of the Invention
This invention relates to level indicating apparatus responsive to pulse coded signals to indicate the equivalent analog amplitude.
The Prior Art
Conventional signal handling systems are known in which analog signals are encoded in pulse form in which they are then recorded or transmitted or otherwise acted upon before being reconverted to analog form. The pulse code has a predetermined arrangement of the pulses according to each analog amplitude. For example, a certain analog signal amplitude range may be divided into a selected number of levels. The number of these levels is determined by the number of bits in the code. If the actual analog signal to be encoded has an amplitude that exceeds the encoding capability of the system, the resulting encoded pulse signal will, when reconverted into analog form, be very distorted.
It is desirable to monitor the amplitude of the analog signal so that the gain of the circuit may be controlled to keep the peak signals within the acceptable range. It is common to provide a meter with a needle to indicate the amplitude of the signal. However, such meters have mechanical inertia that delays their response to short signal pulses and prevents the needle from indicating precisely the amplitude of the signal. Furthermore, it is difficult to cause such meters to retain a signal level indication for a predetermined length of time after the signal has dropped to a lower level. It is also difficult to arrange to have such meters indicate whether peak values of the signal are of positive or negative polarity. Finally, such meters respond to analog signals but not to signals that have been encoded into pulse form.
Level indicating means have been provided to respond to pulse coded signals by applying such signals to suitable logic circuits, such as AND or NAND circuits. Only when the pulse coded signal corresponds to the maximum permissible amplitude of the analog signal, which may be referred to as the saturation level of the analog signal, does the AND or NAND circuit produce an output signal. The output signal may be applied to a lamp or a light emitting diode or the like to indicate that the signal has reached its saturation level. However, even such indicators have the deficiency that they only indicate the saturation level after it has been reached, which makes it difficult to keep the gain of the circuit low enough to keep the analog signal below its saturation level without keeping it at too low a value. Accordingly, it has been common to use such digital indicating apparatus along with a conventional V.U. meter for adjusting the signal level.
It is one object of the present invention to provide improved level indicating apparatus responsive to pulse encoded signals to indicate corresponding analog amplitudes thereof.
It is another object of this invention to indicate saturation levels and the polarity of such saturation levels.
It is another object of this invention to provide a continuous indication of the analog signal level based on the pulse encoded signals.
It is another object of this invention to provide a level indicating apparatus for pulse encoded signals in which the response time to changes in signal level is very fast and the time of retention of the indication is arbitrarily adjustable.